Gross nitrogen mineralization and nitrification rates and their relationships to enzyme activities and the soil microbial biomass in soils treated with dairy shed effluent and ammonium fertilizer at different water potentials

 Gross N mineralization and nitrification rates and their relationships to microbial biomass C and N and enzyme (protease, deaminase and urease) activities were determined in soils treated with dairy shed effluent (DSE) or NH₄ ⁺ fertilizer (NH₄Cl) at a rate equivalent to 200 kg N ha^–1 at three water potentials (0, –10 and –80 kPa) at 20  °C using a closed incubation technique. After 8, 16, 30, 45, 60 and 90 days of incubation, sub-samples of soil were removed to determine gross N mineralization and nitrification rates, enzyme activities, microbial biomass C and N, and NH₄ ⁺ and NO₃ ^– concentrations. The addition of DSE to the soil resulted in significantly higher gross N mineralization rates (7.0–1.7 μg N g^–1 soil day^–1) than in the control (3.8–1.2 μg N g^–1 soil day^–1), particularly during the first 16 days of incubation. This increase in gross mineralization rate occurred because of the presence of readily mineralizable organic substrates with low C : N ratios, and stimulated soil microbial and enzymatic activities by the organic C and nutrients in the DSE. The addition of NH₄Cl did not increase the gross N mineralization rate, probably because of the lack of readily available organic C and/or a possible adverse effect of the high NH₄ ⁺ concentration on microbial activity. However, nitrification rates were highest in the NH₄Cl-treated soil, followed by DSE-treated soil and then the control. Soil microbial biomass, protease, deaminase and urease activities were significantly increased immediately after the addition of DSE and then declined gradually with time. The increased soil microbial biomass was probably due to the increased available C substrate and nutrients stimulating soil microbial growth, and this in turn resulted in higher enzyme activities. NH₄Cl had a minimal impact on the soil microbial biomass and enzyme activities, possibly because of the lack of readily available C substrates. The optimum soil water potential for gross N mineralization and nitrification rates, microbial and enzyme activities was –10 kPa compared with –80 kPa and 0 kPa. Gross N mineralization rates were positively correlated with soil microbial biomass N and protease and urease activities in the DSE-treated soil, but no such correlations were found in the NH₄Cl-treated soil. The enzyme activities were also positively correlated with each other and with soil microbial biomass C and N. The forms of N and the different water potentials had a significant effect on the correlation coefficients. Stepwise regression analysis showed that protease was the variable that most frequently accounted for the variations of gross N mineralization rate when included in the equation, and has the potential to be used as one of the predictors for N mineralization. Received: 10 March 1998     

A field study of gross rates of N mineralization and nitrification and their relationships to microbial biomass and enzyme activities in soils treated with dairy effluent and ammonium fertilizer

Abstract. Gross N mineralization and nitrification rates were measured in soils treated with dairy shed effluent (DSE) (i.e. effluent from the dairy milking shed, comprising dung, urine and water) or ammonium fertilizer (NH₄Cl) under field conditions, by injecting ¹⁵N-solution into intact soil cores. The relationships between gross mineralization rate, microbial biomass C and N and extracellular enzyme activities (protease, deaminase and urease) as affected by the application of DSE and NH₄Cl were also determined. During the first 16 days, gross mineralization rate in the DSE treated soil (4.3–6.1 μg N g^?1 soil day^?1) were significantly (P 14;< 14;0.05) higher than those in the NH₄Cl treated soil (2.6–3.4 μg N g^?1 soil day^?1). The higher mineralization rate was probably due to the presence of readily mineralizable organic substrates in the DSE, accompanied by stimulated microbial and extracellular enzyme activities. The stable organic N compounds in the DSE were slow to mineralize and contributed little to the mineral N pool during the period of the experiment. Nitrification rates during the first 16 days were higher in the NH₄Cl treated soil (1.7–1.2 μg N g^?1 soil day^?1) compared to the DSE treated soil (0.97–1.5 μg N g^?1 soil day^?1). Soil microbial biomass C and N and extracellular enzyme activities (protease, deaminase and urease) increased after the application of the DSE due to the organic substrates and nutrients applied, but declined with time, probably because of the exhaustion of the readily available substrates. The NH₄Cl application did not result in any significant increases in microbial biomass C, protease or urease activities due to the lack of carbonaceous materials in the ammonium fertilizer. However, it did increase microbial biomass N and deaminase activity. Significant positive correlations were found between gross N mineralization rate and soil microbial biomass, protease, deaminase and urease activities. Nitrification rate was significantly correlated to biomass N but not to the microbial biomass C or the enzyme activities. Stepwise regression analysis showed that the variations of gross N mineralization rate was best described by the microbial biomass C and N.     

Effect of cattle slurry in grassland on microbial biomass and on activities of various enzymes

We examined the long-term effects of cattle slurry, applied at high rates, on microbial biomass, respiration, the microbial quotient (qCO₂) and various soil enzyme activities. In March, June, July, and October 1991, slurry-amended grassland soils (0–10 cm) contained significantly higher levels of microbial biomass, N mineralization and enzyme activities involved in N, P, and C cycling. With microbial biomass as the relative value, the results revealed that the slurry treatment influenced enzyme production by the microbial biomass. High levels of urease activity were the result not only of a larger microbial biomass, but also of higher levels of enzmye production by this microbial biomass. The ratio of alkaline phosphatase and xylanase to microbial biomass was nearly constant in the different treatments. The metabolic quotient (qCO₂) declined with increased levels of slurry application. Therefore it appears that microorganisms in slurry-amended soils require less C and energy if there is no competition for nutrients. The results of this study suggest that urease activity, nitrification, and respiration (metabolic quotient) can be used as indicators of environmental stress, produced by heavy applications of cattle slurry.     

Soil microbial biomass, activity and nitrogen transformations in a turfgrass chronosequence

Understanding the chronological changes in soil microbial properties of turfgrass ecosystems is important from both the ecological and management perspectives. We examined soil microbial biomass, activity and N transformations in a chronosequence of turfgrass systems (i.e. 1, 6, 23 and 95 yr golf courses) and assessed soil microbial properties in turfgrass systems against those in adjacent native pines. We observed age-associated changes in soil microbial biomass, CO₂ respiration, net and gross N mineralization, and nitrification potential. Changes were more evident in soil samples collected from 0 to 5 cm than the 5 to 15 cm soil depth. While microbial biomass, activity and N transformations per unit soil weight were similar between the youngest turfgrass system and the adjacent native pines, microbial biomass C and N were approximately six times greater in the oldest turfgrass system compared to the adjacent native pines. Potential C and N mineralization also increased with turfgrass age and were three to four times greater in the oldest vs. the youngest turfgrass system. However, microbial biomass and potential mineralization per unit soil C or N decreased with turfgrass age. These reductions were accompanied by increases in microbial C and N use efficiency, as indicated by the significant reduction in microbial C quotient (qCO₂) and N quotient (qN) in older turfgrass systems. Independent of turfgrass age, microbial biomass N turnover was rapid, averaging approximately 3 weeks. Similarly, net N mineralization was ∼12% of gross mineralization regardless of turfgrass age. Our results indicate that soil microbial properties are not negatively affected by long-term management practices in turfgrass systems. A tight coupling between N mineralization and immobilization could be sustained in mature turfgrass systems due to its increased microbial C and N use efficiency.     

Soil microbial biomass, activity and potential nitrogen mineralization in a pasture: Impact of stock camping activity

Grazing animals recycle a large fraction of ingested C and N within a pasture ecosystem, but the redistribution of C and N via animal excreta is often heterogeneous, being highest in stock camping areas, i.e., near shade and watering sources. This non-uniform distribution of animal excreta may modify soil physical and chemical attributes, and likely affect microbial community eco-physiology and soil N cycling. We determined microbial population size, activity, N mineralization, and nitrification in areas of a pasture with different intensity of animal excretal deposits (i.e., stock camping, open grazing and non-grazing areas). The pasture was cropped with coastal bermudagrass (Cynodon dactylon L.) and subjected to grazing by cattle for 4 y. Soil microbial biomass, activity and N transformations were significantly higher at 0-5 cm than at 5-15 cm soil depth, and the impacts of heterogeneous distribution of animal excreta were more pronounced in the uppermost soil layer. Microbial biomass, activity and potential net N mineralization were greater in stock camping areas and were significantly correlated (r²≈0.50, P<0.05) with the associated changes in total soil C and N. However, gross N mineralization and nitrification potential tended to be lower in stock camping areas than in the open grazing areas. The lower gross N mineralization, combined with greater net N mineralization in stock camping areas, implied that microbial N immobilization was lower in those areas than in the other areas. This negative association between microbial N immobilization and soil C is inconsistent with a bulk of publications showing that microbial N immobilization was positively related to the amount of soil C. We hypothesized that the negative correlation was due to microbial direct utilization of soluble organic N and/or changes in microbial community composition towards active fungi dominance in stock camping areas.     

三峡库区不同林龄柑橘土壤酶活性的演变

土壤酶驱动土壤生态系统养分的循环和控制生态系统的功能。本研究以生长年限为10、20年和30年的柑橘林0~20 cm和20~40 cm土层土壤为研究对象,主要探讨了土壤脲酶、转化酶和过氧化氢酶活性随着柑橘林龄的延长和土壤深度的增加的变化规律。结果表明,随着柑橘林龄的延长,0~20 cm土层土壤过氧化氢酶活性10年和20年样地之间无显著性差异,但都显著大于30年的样地;而0~20 cm土层土壤转化酶和脲酶活性逐渐提高,20年时达到最大值,其后又降低。随着土壤深度的增加,过氧化氢酶、转化酶和脲酶活性在3个林龄的柑橘林中都呈现显著的下降趋势。相关性分析的结果表明,土壤转化酶活性、脲酶活性都与土壤有机碳和微生物量碳氮之间都具有显著的正相关性,而过氧化酶氢活性与土壤理化特性及其微生物量之间都无显著的相关性。主成分分析结果进一步显示,土壤转化酶活性、脲酶活性、有机碳和微生物生物量碳氮均在第一主成分中具有较大的载荷,对第一主成分的贡献最大。以上结果表明脲酶和转化酶活性能够做为柑橘土壤质量变化的敏感指标。     

连年翻压绿肥对植烟土壤微生物量及酶活性的影响

通过3年田间定位试验,研究连年翻压绿肥对植烟土壤微生物量碳、氮及酶活性的影响。结果表明,连年翻压绿肥能提高土壤微生物量碳、氮及土壤脲酶、酸性磷酸酶、蔗糖酶、过氧化氢酶的活性,且随翻压年限的增加而增加。整个生育期,翻压3年绿肥的处理与对照相比微生物量碳、氮分别提高31.0%~67.1%、23.0%~145.1%;土壤脲酶、酸性磷酸酶、蔗糖酶、过氧化氢酶活性分别提高34.4%~51.9%、11.0%~18.6%、58.0%~172.7%、24.0%~50.0%,表明翻压绿肥后土壤生物过程活跃,利于有机物质的转化和烤烟正常生长所需的营养供应。动态变化特征表明,翻压绿肥1、2、3年的各处理微生物量碳、氮均在团棵期出现峰值,土壤脲酶、酸性磷酸酶、过氧化氢酶均在旺长期出现峰值。在出现峰值时翻压3年的处理与对照相比微生物量碳、氮分别提高67.1%、60.7%;土壤脲酶、酸性磷酸酶、过氧化氢酶活性分别提高51.9%、14.2%、30.6%。此时正值生育旺期,利于烟株生长发育,说明连年翻压绿肥后培肥土壤效果显著。土壤微生物量C、N和酶活性能灵敏反映土壤肥力的变化,可作为评价土壤质量的生物学指标。     

Biochemical characterization of urban soil profiles from Stuttgart, Germany

The knowledge of biochemical properties of urban soils can help to understand nutrient cycling in urban areas and provide a database for urban soil management. Soil samples were taken from 10 soil profiles in the city of Stuttgart, Germany, differing in land use—from an essentially undisturbed garden area to highly disturbed high-density and railway areas. A variety of soil biotic (microbial biomass, enzyme activities) and abiotic properties (total organic C, elemental C, total N) were measured up to 1.9 m depth. Soil organic matter was frequently enriched in the subsoil. Microbial biomass in the top horizons ranged from 0.17 to 1.64 g C kg⁻¹, and from 0.01 to 0.30 g N kg⁻¹, respectively. The deepest soil horizon at 170-190 cm, however, contained 0.12 g C kg⁻¹ and 0.05 kg N kg⁻¹ in the microbial biomass. In general, arylsulphatase and urease activity decreased with depth but in three profiles potentially mineralizable N in the deepest horizons was higher than in soil layers directly overlying. In deeply modified urban soils, subsoil beside topsoil properties have to be included in the evaluation of soil quality. This knowledge is essential because consumption of natural soils for housing and traffic has to be reduced by promoting inner city densification.     

Long-term application of compost influences microbial biomass and enzyme activities in a tropical Aeric Endoaquept planted to rice under flooded condition

In a field study, long-term application of compost to a tropical Aeric Endoaquept under continuous rice growing in a rice-rice-fallow sequence resulted in the stimulation of microbial biomass and select soil enzyme activities. Mean seasonal soil microbial biomass-C (C_mic) increased by 42%, 39% and 89% in inorganic fertilizer, compost and compost+inorganic fertilizer treatments, respectively, over the unamended control. C_mic content was also influenced by the rice crop growth stage and was highest at maximum tillering stage irrespective of treatments and declined thereafter. Soil organic C (C_org) content showed highly significant positive correlation with dehydrogenase, urease, cellulase, β-glucosidase and fluorescein di-acetate (FDA) hydrolysis activity, and a positive but not significant correlation with invertase and amidase activity. C/N ratio which was lowest in unamended control plots showed a significant positive relationship with only the enzymes involved in C cycle. Stepwise regression analysis revealed that for prediction of both total organic C and total N, FDA hydrolysis activity contributed significantly for the variance and explained up to 85-96% variability. Results demonstrated that microbial biomass and soil enzyme activity is sensitive in discriminating between long-term organic residue amendment practices.     

Response of microbial characteristics to heavy metal pollution of mining soils in central Tibet,China

Soil microbial activity plays a crucial role in soil microbiological processes, which can be used as a useful indicator to determine the ecological effects of heavy metal pollution on soils. The objective was to determine the effects of heavy metal pollution on mining soils at the Lawu mine of central Tibet, China on soil enzyme activities (sucrase, urease and acid phosphatase), microbial biomass C, N and P (MBC, MBN, and MBP), basal respiration, metabolic quotients, and N mineralization. Sixteen soil samples around the mine were sampled, and one soil sample, 2 km from the mine center, was taken as the control. Compared to the control, mining soils were polluted by heavy metals, Cu, Zn, Pb and Cd, resulting in decreases of sucrase activities, urease activities, acid phosphatase activities, MBC, MBN, MBP, and N mineralization, and increases of basal respiration and qCO₂. Multivariate analysis (cluster analysis [CA], principle component analysis [PCA] and canonical correlation analysis [CCA]) indicated nine microbial variables were only reduced to one principal component explaining 72% of the original variances, and MBC (R² = 0.93) had the highest positive loadings on the principal component. Mining soils polluted by heavy metals were perfectly clustered into four groups, which were highly distinguished by MBC. There were significant canonical correlations between soil heavy metals and microbial indexes on two canonical variates (R1 = 0.99, p < 0.001; R2 = 0.97, p < 0.01), which further demonstrated significant correlations between soil heavy metal contents and microbial characteristics. Hence, our results suggested that MBC may be used a sensitive indicator for assessing changes in soil environmental quality in metal mine of central Tibet.     

Enzymatic activities and microbial biomass in soil as influenced by metalaxyl residues

A laboratory experiment was conducted to study the impact of metalaxyl application at different concentration levels on microbial biomass and the biochemical activities in soil. A dissipation study of metalaxyl highlighted 52.5-56.8% loss of metalaxyl due to the presence of microbial activity. However, a small but significant decline in microbial biomass was observed on 60 d of incubation period. Metalaxyl showed a highly significant effect in decreasing total N and organic C content in soil from 0 to 30 d of incubation. Dehydrogenase, phosphatase, urease, arylsulphatase and β-glucosidase activities were monitored in metalaxyl treated soils. Except urease, all the enzymatic activities initially increased and then decreased. Urease activity showed a continuous gradual decrease throughout the experimental period. Thus, metalaxyl might influence the growth and development of crop-plants, since it has direct impact on nutrient recycling and energy flow in soil.     

Nitrogen mineralization,N<Subscript>2</Subscript>O production and soil microbiological properties as affected by long-term applications of sewage sludge composts

A field study was conducted to investigate the long-term effect of surface application of sewage sludge composts vs chemical N fertilizer on total N, total C, soluble organic C, pH, EC, microbial biomass C and N, protease activity, deaminase activity, urease activity, gross and net rates of N mineralization and nitrification, CO₂ evolution, and N₂O production. Soil samples were taken from five depths (0–15, 15–20, 20–30, 30–40, and 40–50 cm) of a long-term experiment at the University of Tokyo, Japan. Three fields have been receiving sewage sludge composted with rice husk (RH), sawdust (SD), or mixed chemical fertilizer NPK (CF), applied at the rate of 240 kg N ha^–1 each in split applications in summer and autumn since 1978. Significantly higher amounts of total N and C and soluble organic C were found in the compost than in the CF treatments up to the 40-cm soil depth, indicating improved soil quality in the former. In the CF treatment, soil pH values were significantly lower and electrical conductivity values were significantly higher than those of compost-treated soils of up to 50 cm depth. Soil microbial biomass C and N, CO₂ evolution, protease, deaminase, and urease activities were significantly higher in the compost than in the CF treatments due to greater availability of organic substrates that stimulated microbial activity. Gross N mineralization rates determined by ¹⁵N dilution technique were eight and five times higher in the SD and RH treatments than in the CF treatment, respectively, probably due to high levels of microbial and enzyme activities. Net N mineralization rates were also significantly higher in the compost treatments and were negative in the CF treatment indicating immobilization. Net nitrification rates were higher in compost treatments and negative in the CF treatment. Nitrous oxide productions from compost treatments were higher than the CF treatment due to the greater availability of mineral N as a result of higher mineralization and nitrification rates and soluble organic C in the former. Most of the measured parameters were highest in the surface soil (0–15 cm) and were significantly higher in the SD treatment than in the RH treatment.     

Tree species effects on soil enzyme activities through effects on soil physicochemical and microbial properties in a tropical montane forest on Mt. Kinabalu, Borneo

Tree species influence on the soil mineralization process can regulate overall nutrient cycling in a forest ecosystem, which may occur through their effects on substrate quality, soil physicochemical properties and soil microbial community. We investigated tree species effects on soil enzyme activities in a tropical montane forest on Mt. Kinabalu, Borneo. Specifically, we analyzed C- and P-degrading enzyme activities, as well as the relationships among the enzyme activities, soil physicochemical properties, substrate quality (C, N, and P concentrations), and microbial composition in the top 5 cm soils beneath conifers (Dacrycarpus imbricatus and Dacrydium gracilis) and broadleaves (Lithocarpus clementianus, Palaquium rioence, and Tristaniopsis clementis). Activities of acid phosphatase and β-d-glucosidase were significantly different among the tree species. Soil moisture, total C and N content and microbial lipid abundance (a proxy for microbial composition) could influence the enzyme activities although the relative contributions of microbial composition to the enzyme activities might be smaller. A higher acid phosphatase activity beneath Dacrydium than those beneath the other tree species can compensate for a lower concentration of P in available fractions beneath Dacrydium. This localized mineralization activity could subsequently influence soil nutrient availability in this forest.     

Non-linear response of microbial activity across a gradient of nitrogen addition to a soil from the Gurbantunggut Desert,northwestern China

Identifying the patterns of soil microbial responses to increasing nitrogen (N) availability are important since microbial processes are related to the potential nutrient transformations. The effects of the addition of N to the soil microbial community of the Gurbantunggut Desert, China, are described in this paper. The study was conducted over a two-year period with trials commencing at the beginning of each growing season. Soil enzyme activity, microbial biomass and microbial community level physiological profile (CLPP) were determined at 0–5 cm and 5–10 cm soil depths. Nitrogen was added to the soil at five rates plus a control, i.e. 0, 0.5, 1, 3, 6 and 24 g N m⁻² y⁻¹. We hypothesized that soil enzyme activities and microbial biomass N (MBN) would firstly increase and then decrease, and CLPP would be altered with increasing N addition, due to the deleterious effects of higher N addition upon microbial activity. Because of the relatively higher organic matter in the upper depth of soil layers, we further hypothesized that the responses of microbial activities in the 0–5 cm depth would be more marked than at 5–10 cm. In partial support of our hypothesis, soil enzyme activities, microbial biomass and nutrient concentrations responded to N addition with the most significant changes occurring in the 0–5 cm soil depth. Addition of N resulted in an increase in MBN and a decrease in urease activity. Invertase and alkaline phosphatase (AlP) activities increased at low doses of N addition and showed a decrease at higher doses. There was no evidence of change in oxidative enzyme activity at low N treatments but activity decreased at high N additions. However, the CLPP was not affected by N addition. The results of this study suggest that N supplementation in this desert soil may affect C transformation, increase availability of N and P, and immobilize N in the microbial biomass. Responses of the enzyme activity to N supplementation occurred within the context of an apparently stable or unresponsive microbial community structure.     

Role of soil drying in nitrogen mineralization and microbial community function in semi-arid grasslands of north-west Australia

We examined effects of wetting and then progressive drying on nitrogen (N) mineralization rates and microbial community composition, biomass and activity of soils from spinifex (Triodia R. Br.) grasslands of the semi-arid Pilbara region of northern Australia. We compared soils under and between spinifex hummocks and also examined impacts of fire history on soils over a 28 d laboratory incubation. Soil water potentials were initially adjusted to −100 kPa and monitored as soils dried. We estimated N mineralization by measuring changes in amounts of nitrate (NO₃⁻-N) and ammonium (NH₄⁺-N) over time and with change in soil water potential. Microbial activity was assessed by amounts of CO₂ respired. Phospholipid fatty acid (PLFA) analyses were used to characterize shifts in microbial community composition during soil drying. Net N mineralized under hummocks was twice that of open spaces between hummocks and mineralization rates followed first-order kinetics. An initial N mineralization flush following re-wetting accounted for more than 90% of the total amount of N mineralized during the incubation. Initial microbial biomass under hummocks was twice that of open areas between hummocks, but after 28 d microbial biomass was<2 μ g⁻¹ ninhydrin N regardless of position. Respiration of CO₂ from soils under hummocks was more than double that of soils from between hummocks. N mineralization, microbial biomass and microbial activity were negligible once soils had dried to −1000 kPa. Microbial community composition was also significantly different between 0 and 28 d of the incubation but was not influenced by burning treatment or position. Regression analysis showed that soil water potential, microbial biomass N, NO₃⁻-N, % C and δ¹⁵N all explained significant proportions of the variance in microbial community composition when modelled individually. However, sequential multiple regression analysis determined only microbial biomass was significant in explaining variance of microbial community compositions. Nitrogen mineralization rates and microbial biomass did not differ between burned and unburned sites suggesting that any effects of fire are mostly short-lived. We conclude that the highly labile nature of much of soil organic N in these semi-arid grasslands provides a ready substrate for N mineralization. However, process rates are likely to be primarily limited by the amount of substrate available as well as water availability and less so by substrate quality or microbial community composition.     

沙漠腹地咸水滴灌林地土壤养分、微生物量和酶活性的典型相关关系

鉴于塔里木沙漠公路防护林所处环境条件和管理模式的特殊性及在南疆社会、经济发展中的重要性,试验选择四种不同矿化度(2.58、5.75、8.90、13.99 g L-1)水滴灌的防护林地,采集0~5 cm、5~15cm、15~30 cm、30~50 cm四层土样为研究材料,主要采用典型相关分析法,对防护林地土壤养分因子、微生物量因子和酶活性因子中每两组变量间的相关性进行了分析。结果表明:三组变量土壤养分、微生物量、酶活性中,每两者之间均有显著的典型相关变量存在,而且基本能够代表变量总体相关信息;土壤养分与土壤微生物量的相关性主要由养分中的全氮、速效氮、有机质、全磷含量和土壤微生物量中的放线菌数量、微生物量碳和微生物量磷引起的;土壤养分与土壤酶活性的相关性主要由土壤有机碳、速效钾含量与土壤过氧化氢酶、磷酸酶活性的相关性引起;土壤微生物量与土壤酶活性的相关性主要由土壤微生物量磷、微生物量氮与土壤蔗糖酶、磷酸酶活性的相关性引起;滴灌水矿化度对塔里木沙漠公路防护林地土壤养分和微生物量的效应明显,高矿化度水不利于土壤养分积累和微生物生存。     

Changes in enzyme activities and soil microbial community composition along carbon and nutrient gradients at the Franz Josef chronosequence, New Zealand

During primary succession, the abundance of carbon (C) and nitrogen (N) in soil increases, while phosphorus (P) declines. These changes in nutrient concentrations in organic matter are likely to play an important role in controlling enzyme-mediated nutrient mineralization. We examined how enzyme activity and efficiency changed with successional time in organic and mineral soils taken from the 120 000-year-old Franz Josef soil development sequence, New Zealand, and the relationship between enzyme activity and efficiency and soil nutrient concentrations. We found that the activity of enzymes involved in P mineralization increased with site age across the Franz Josef chronosequence, while the activity of enzymes regulating C and N mineralization declined in organic but not mineral soil. Sulfatase activity peaked at an intermediate-aged site, possibly indicating a transient period of S limitation. The activity of phosphatase enzymes was negatively correlated with the concentration of P in the soil, whereas activity of C-, N- and S-hydrolyzing enzymes was not strongly dependent on nutrient concentrations. When assessed as efficiency (activity per unit microbial biomass), there were strong patterns of increasing efficiency of P-, and decreasing efficiency of C- and N-hydrolyzing enzymes with site age. We suggest that activity patterns for C-, N- and S-hydrolyzing enzymes were obscured by simultaneous and opposing changes in enzyme efficiency and microbial biomass. In mineral soil, efficiency of enzymes was negatively correlated with soil nutrient availability. In contrast, in organic soil, efficiency of C-, N- and S-hydrolyzing enzymes was positively correlated with soil P, while efficiency of P-hydrolyzing enzymes was negatively correlated with soil P. The increase in efficiency of P-hydrolyzing enzymes, and decrease in efficiency of C-, N- and S-hydrolyzing enzymes with site age was accompanied by a shift in microbial community composition towards higher relative abundances of fungi. Changes in enzyme efficiency with site age are likely to be due to both constitutive differences in enzyme production, and down-regulation of enzyme expression.     

Appropriate nitrogen supply could improve soil microbial and chemical characteristics with Sophora davidii seedlings cultivated in water stress conditions

Abstract

A greenhouse experiment was conducted to investigate the changes of soil microbial activities and chemical properties under different water and nitrogen (N) supply conditions. A completely randomized design was subjected to three water regimes (80%, 40% and 20% water field capacity (FC)) and three N supply regimes (control, N0: 0 mg N kg^?1 soil; low N supply, Nl: 92 mg N kg^?1 soil; and high N supply, Nh: 184 mg N kg^?1 soil) by potting with 2-month-old Sophora davidii seedlings. Water stress decreased the content of soil organic carbon (C), available N and phosphorus (P), the ratio of C/N, the ratio of C/P, as well as activities of soil invertase, urease and alkaline phosphatase, but not reduced microbial biomass C, N and P contents. Soil microbial and chemical characteristics also exhibited strong responses to N supply, and these responses were inconsistent among N supply levels. The contents of soil organic C and available P showed stronger positive responses to Nl than to Nh, while the available N content increased with increasing N supply. Additionally, Nl rather than the other two N treatments led to increased microbial biomass N and invertase activity under 20% FC treatment, even though the invertase activity increased in Nh treatment under 40% FC and 80% FC treatments. Nl treatment also increased the C/P ratio and alkaline phosphatase activity. These results suggest that water and N co-limited nutrient mineralization and microbial activity, and that these characteristics responded positively to Nl. Therefore, appropriate or low N supply is recommended to increase soil quality restrained by water stress, thereby facilitating S. davidii seedling establishment under water deficit conditions.     

有机和常规生产模式下菜田土壤酶活性差异研究

通过对露地及温室环境下有机和常规蔬菜栽培土壤采样,测定分析了5种参与土壤碳氮循环的酶活性,及其与土壤相关理化性质之间的关系。结果显示:温室及露地土壤EC值在有机生产中相应低于常规生产12%和16%;有机生产土壤微生物碳氮含量显著高于常规生产;不同生产模式下土壤酶活性差异显著,有机生产土壤中的蛋白酶、脲酶、脱氢酶、β-葡糖苷酶活性高于常规生产,而硝酸还原酶活性较常规生产低;有机与常规栽培对蛋白酶活性影响极显著(P=0.006 8),对脲酶活性影响程度达显著水平(P=0.012 4)。除脱氢酶以外,不同栽培模式环境对土壤中另外4种酶活性均有显著影响,温室栽培环境中的蛋白酶、脲酶和硝酸还原酶活性高于露地。除硝酸还原酶外,其他4种酶活性与可溶性全氮、微生物碳、微生物氮相关系数达到显著水平。分析表明,土壤酶活性受到栽培方式以及环境的影响,并且有机生产能够提高参与土壤碳氮循环的酶活性。土壤蛋白酶、脲酶、脱氢酶和β-葡糖苷酶活性能够作为表征土壤碳氮循环以及微生物活性的指标。     

Microbial activities in forest soils exposed to chronic depositions from a lignite power plant

Atmospheric emissions of fly ash and SO₂ from lignite-fired power plants strongly affect large forest areas in Germany. The impact of different deposition loads on the microbial biomass and enzyme activities was studied at three forest sites (Picea abies (L.) Karst.) along an emission gradient of 3, 6, and 15 km downwind of a coal-fired power plant (sites Ia, II, and III, respectively), representing high, moderate and low emission rates. An additional site (site Ib) at a distance of 3 km from the power plant was chosen to study the influence of forest type on microbial parameters in coniferous forest soils under fly ash and SO₂ emissions. Soil microbial biomass C and N, CO₂ evolved and activities of l-asparaginase, l-glutaminase, β -glucosidase, acid phosphatase and arylsulfatase (expressed on dry soil and organic C basis) were determined in the forest floor (L, Of and Oh horizon) and mineral top soil (0-10 cm). The emission-induced increases in ferromagnetic susceptibility, soil pH, concentrations of mobile (NH₄NO₃ extractable) Cd, Cr, and Ni, effective cation exchange capacity and base saturation in the humus layer along the 15 km long transect significantly (P<0.05) reflected the effect of past depositions of alkaline fly ash. Soil microbial and biochemical parameters were significantly (P<0.05) affected by chronic fly ash depositions. The effect of forest type (i.e. comparison of sites Ia and Ib) on the studied parameters was generally dominated by the deposition effect. Alkaline depositions significantly (P<0.05) decreased the microbial biomass C and N, microbial biomass C-to-N ratios and microbial biomass C-to-organic C ratios. Microbial respiration, metabolic quotient (qCO₂) and the activities of l-asparaginase, l-glutaminase, β-glucosidase, acid phosphatase and arylsulfatase were increased by long-term depositions from the power plants. Acid phosphatase had the highest specific (enzyme activities expressed per unit organic C) activity values among the enzymes studied and arylsulfatase the lowest. The responses of the microbial biomass and soil respiration data to different atmospheric deposition loads were mainly controlled by the content of organic C and cation exchange capacity, while those of enzyme activities were governed by the soil pH and concentrations of mobile heavy metals. We concluded that chronic fly ash depositions decrease litter decomposition by influencing specific microbial and enzymatic processes in forest soils.